Renewable Energy Storage Methods and Systems

ABSTRACT

In one embodiment, a renewable energy storage system includes a forward osmosis system, a hydro-turbine, and a separation (e.g., CEDI) system powered by one or more natural regenerating energy sources, such as wind or solar. In another embodiment, a renewable energy storage system includes a forward osmosis system, a hydro-turbine, a solar thermal heat exchanger through which the diluted osmotic draw solution can be directed for purposes of heating up the draw solution, and a solvent-water separator configured to separate the draw solution from the water. One example method includes drawing water across a forward osmosis membrane in a forward osmosis system such that the water drawn across the membrane dilutes an osmotic draw solution; directing the diluted osmotic draw solution to drive a hydro-turbine to produce energy; and separating the water from the draw solution using one or more natural regenerating energy sources.

CORRESPONDING PATENT APPLICATIONS

The present application claims priority from provisional application Ser. No. 62/417,864, filed Nov. 4, 2016, the entire contents of which is incorporated herein in its entirety by reference.

BACKGROUND

A cost-effective energy storage technology, at low cost kWh cycle, and capable of rapid ramp-up, and combined with large scale installations of renewable energy, is needed to equalize grid loads throughout the day, for residential, commercial and utility-scale customers. The cost/kWh/cycle metric includes device costs, balance of system (BOS) costs, round trip efficiency (RTE) rates, long-term maintenance requirements, current rates, and the number of cycles that the device can store and discharge electricity, etc.

Forward osmosis (FO) reflects recent technology being explored for desalination of seawater and produced water from oil and gas fields. Unlike reverse osmosis (RO) processes, which employ high pressures ranging from 400-1100 psi to drive fresh water through the membrane, forward osmosis uses the natural osmotic pressures of salt solutions to effect fresh water separation. A draw solution, having a significantly higher osmotic pressure than the saline feed-water, flows along the permeate side of the membrane, and water naturally transports itself across the membrane by osmosis. FO also does not require extensive pretreatment, given that the low pressures minimize fouling of the membranes.

SUMMARY

Embodiments of the present invention employ forward osmosis in combination with natural regenerating energy sources as a unique way to create renewable energy storage. In one embodiment, a renewable energy storage system comprises a forward osmosis system for drawing water across a membrane such that, when in use, the water drawn across the membrane is used to dilute an osmotic draw solution and the diluted osmotic draw solution is used to drive a hydro-turbine to produce energy; a hydro-turbine driven by the diluted draw solution when in use, and a separation system, such as an electro-deionization (EDI) system, or more particularly a continuous electro-deionization (CEDI) system, for separating the drawn water from the draw solution, the separation (e.g., CEDI) system powered by one or more natural regenerating energy sources, so that the draw solution can be re-directed to the forward osmosis system and the water can be reused to be drawn across the forward osmosis membrane. The one or more natural regenerating energy sources preferably comprise either solar energy and/or wind energy. In some embodiments, the renewable energy storage system further comprises a second hydro-turbine. With some embodiments, the draw solution comprises one or more ionic osmotic solutions, and in some cases, magnesium chloride and/or ammonia chloride specifically, although others can be used. In some embodiments, the forward osmosis system comprises a pressure-retarded forward osmosis system.

In alternative embodiments, a renewable energy storage system is provided comprising a forward osmosis system for drawing water across a membrane such that, when in use, the water drawn across the membrane is used to dilute an osmotic draw solution and the diluted osmotic draw solution is used to drive a hydro-turbine to produce energy; a hydro-turbine driven by the diluted draw solution when in use; a solar thermal heat exchanger through which the diluted osmotic draw solution can be directed for purposes of heating up the draw solution to cause substantial separation of the draw solution from the water, and a solvent-water separator configured to separate the draw solution from the water so that the draw solution can be re-directed to the forward osmosis system and the water can be reused to be drawn across the forward osmosis membrane. In some embodiments, the renewable energy storage system further comprises a second hydro-turbine. In some embodiments, the forward osmosis system comprises a pressure-retarded forward osmosis system. The draw solution preferably comprises a cloud point osmotic solution, and preferably one or more cloud point glycols, many examples of which are identified in several patent disclosures incorporated by reference herein below.

Embodiments of the present invention also include methods of storing renewable energy comprising, in one example, drawing water across a forward osmosis membrane in a forward osmosis system such that the water drawn across the membrane dilutes an osmotic draw solution; directing the diluted osmotic draw solution to drive a hydro-turbine to produce energy; and separating the water from the draw solution using one or more natural regenerating energy sources so that the draw solution can be re-directed to the forward osmosis system and the water can be reused to be drawn across the forward osmosis membrane. In one embodiment, separating the water from the draw solution comprises directing the diluted draw solution into an separation system, such as an EDI or CEDI system, powered by the one or more natural regenerating energy sources, where the one or more natural regenerating energy sources comprises either solar energy and/or wind energy.

In an alternative embodiment, separating the water from the draw solution comprises directing the diluted draw solution through a solar thermal heat exchanger for purposes of heating up the draw solution to cause substantial separation of the draw solution from the water, and then directing the diluted draw solution into a solvent-water separator configured to separate the draw solution from the water. In either case, embodiments may further comprise directing the water through a second hydro-turbine before re-directing the water to the forward osmosis system, and in some cases, the forward osmosis system may comprise a pressure-retarded forward osmosis system.

BRIEF DESCRIPTION OF THE FIGURES

The aforementioned objects and advantages of the present invention, as well as additional objects and advantages thereof, will be more fully understood hereinafter as a result of a detailed description of a preferred embodiment when taken in conjunction with the following drawings in which:

FIG. 1 shows a schematic view of one embodiment of the present invention;

FIG. 2 shows a schematic view of an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The present invention embodiments take advantage of the very low energy requirements of a forward osmosis system for water desalination or purification, combined with a continuous electrodeionization system with improved high-conductivity membranes, for production of fresh water and regeneration of the draw solution for the forward osmosis cycle. If an electro-deionization (EDI) process is supplemented downstream to a forward osmosis (FO) process, the energy consumption of EDI remains within manageable levels, given that the desalination is primarily effected by the FO membranes and the electrolyte still retains sufficient electrochemical conductivity for movement of ions, without inordinate resistance or concentration polarization effects. In addition, the problem of membrane fouling or resin fouling is alleviated, given that only the diluted draw solution is fed to the EDI process, without organics, calcium and magnesium carbonates/bicarbonates, and other fouling contaminants in the feed to the EDI. The end result is a very low volume of concentrated brine (˜25%) as the effluent, ideal for re-use as the draw solution concentrate for the upstream FO process. and with almost 70-75% of the incoming permeate from the FO process, as the diluted draw solution, converted to water treated to environmentally useable levels.

Any ionized salt which gives a high osmotic potential in its solution in water, can be used as the draw solution for the forward osmosis process. Examples of preferred salts include ammonium chloride, magnesium chloride, ammonium bicarbonate or ammonium carbonate. A 20% solution of MgCl₂ yields an osmotic pressure of almost 300 atms, as compared to 168.54 atms for an equivalent concentration of NaCl. Similarly, ammonium chloride solutions have even higher osmotic potentials, and would be very suitable draw agents for the FO process, while also retaining high electrochemical conductivity for a downstream separation process, such as a continuous electro-deionization (CEDI) process. Forward osmosis, using for example ionic salts as the draw solute, enables substantially pure water-salt solutions to be sent down-stream to the EDI process, which alleviates membrane fouling and associated maintenance issues in the EDI system. Thus, the EDI process works at close to ideal efficiency.

CEDI also includes anionic and cationic exchange resins in the main electrode compartments, in addition to the anionic and cationic membranes lining the periphery of the cells. As the salts ions are transported across the respective membranes, typically at a voltage of around 0.4-0.6 V/cell, the conductivity of the solution decreases, leading to higher amperage needs and corresponding resistance effects. Operating the cell at a higher voltage, around 0.8 V/cell, allows water to break down into H+ and OH— ions, which interact with the ion exchange resins in the cell, and restore ionic conductivity in the solution. The applied voltage is insufficient to electrolyze water into hydrogen and oxygen gases, which would ideally require voltages in excess of 1.23 VDC. Thus, the resins acts as a ionic pathway across each individual cell, keeping cell amperage and resistance low. The process is termed continuous because the resins continuously get regenerated, thus, there is no need for electrode polarity reversal, and product output is constant. Typical operating numbers for a CEDI system, operating downstream of a dual RO system, to produce ultra-pure water for power generation or applications in semi-conductor manufacture, are a product rate of 9 m³/hr, for a CEDI power supply of 300 V, 16 A. This leads to a energy requirement of 0.53 kWh/m³ for highly purified water.

Commercially available solid polymer membranes do not have sufficient electrochemical conductivity for efficiently deionizing large amounts of salt without a substantial energy penalty. New membranes with electrochemical conductivity higher by a hundred-fold are described herein. Such membranes, suitable for deionization of the ionic FO permeate to pure water and regeneration of a concentrated ionic FO draw solution, are described herewith. Porous gelled liquid electrolyte membranes have properties intermediate between liquid electrolytes and solids-state electrolyte membranes. These membranes have interconnected pores, filled with the desired electrolyte, which is held inside the pores by capillary forces. The pores are typically between 1-10 microns, and the porous polymer gel may have a porosity between 85-90%, which can then be filled with the desired liquid electrolyte by absorption. The polymers typically used for forming the porous membrane structures are well-known in literature, and range from polyethylene oxide (PEO), polyacrylonitrile (PAN), polydimethylsiloxane (PDMS), polyvinylidene difluoride (PVDF), poly(methyl-methlyacrylate) (PMMA) and other polymers. Some membranes cited in literature are also made from mixtures of these polymers with each other and other polymers. Thus, a few examples of porous membrane structures suitable for gelled electrolyte membranes are PVDF-HFP (PVDF-co-hexafluoropropylene) membranes, PDMS-PAN-PEO membranes, PVDF-NMP-EC-PC (PVDF with n-methylpyrilodine and ethylene and propylene carbonate) and even PVDF on glass mats. Such porous membranes, in which saturated solutions of MgCl₂ or NH₄Cl have been absorbed, would have much higher electrochemical conductivity than conventional solid-state membranes.

If the draw solution to be used for the FO process is MgCl₂, a porous gelled electrolyte membrane filled with saturated MgCl₂ solution can be used for both the anionic and the cationic sides in the CEDI process, instead of conventional anionic or cationic solid membranes. Given that the gelled MgCl₂ cationic membrane is now used for transport of Mg+ ions across the membrane in the CEDI system, and the gelled MgCl₂ anionic membrane is used for transport of chloride ions across the membrane in the CEDI system, the transport efficiency of these ions across their respective membranes are optimized. Such gelled polymer electrolyte membranes function as salt bridges with electrodes of suitable polarity attached to them to either enable anion or cation transport. No new species are introduced into the system, and no other electrochemical or ionic interference effects takes place, given that all the cells in the CEDI system contain the same ionic species, though in different concentrations. The exact impedance matching of these gelled polymer electrolyte membranes, if made by a procedure as described above, enables the minimization of polarization losses in the experimental cell. The anode and cathode materials are platinized titanium meshes, in order to resist salt and chloride corrosion.

Other osmotic solutions can also be used for forward osmosis. Some, known as ‘cloud-point’ solutes, are organic solutions in water, exhibiting high osmotic potentials, and have the property of solubility inversion at certain temperatures. Thus, at these ‘cloud-point’ tempratures, the organic solutes exhibit hydrophibicity and, thus, fall out of solution from its water solvent mixture. A two-phase mixture results, one solute-rich and the other water-rich.

The FO process can make use of these novel organic, hydrophilic-lypophilic, specifically engineered oligomers, capable of high osmotic pressures in aqueous solutions and, thus, able to extract water from saline waters (seawater, brackish water, water from hydraulic fracturing operations in the oil and gas sectors like ‘frac blowback water’ and ‘produced water’, and industrial waste waters), with high recovery rates. The regeneration of these ‘osmotic agents’ is effected by the ‘cloud-point’ phenomena, which causes a phase separation of these agents from their aqueous solutions with increases in temperature. Utilization of solar-thermal systems can effectively enable the temepratures of the solute-water mixtures to be rasied above the ‘cloud-point’ temperatures, thus, enabling regneration of the concentrated ‘cloud-point’ solutes for recyling to the FO step.

Several prototype polymers were designed, synthesized and tested for osmotic potentials against 20% MgCl₂ solutions (osmotic pressure=300 atm). These co-polymers, essentially branched polyethylene glycols with end groups ranging from polypropylene glycols to polybutylene glycols, have an interesting property of cloud-point solubility inversion at certain critical temperatures, resulting in a two-phase media, one water-rich and the other polymer-rich. These co-polymers have a very high intrinsic osmotic pressure, and thus are very efficient draw solutes in an FO process.

A patent on an inventive NRGTEK FO process describes use of organic, hydrophilic-lypophilic, specifically-engineered, co-polymers, capable of high osmotic pressures in aqueous solutions, which are able to extract water from saline waters with high recovery rates. In that regard, reference is made to U.S. Pat. No. 8,021,553, issued on Sep. 20, 2011, the entire contents of which is incorporated herein by reference. The regeneration of these ‘osmotic agents’ is achieved by their ‘cloud-point’ phenomena, which causes a phase separation (solubility inversion) of these osmotic agents from their aqueous solution with increases in temperature. NRGTEK has been able to initiate cloud-point separation by specifically engineering these polymers, as well as by addition of cloud-point depression agents, post-FO processing, to within 1.5°-2° C. of the inlet saline water stream. Given that water essentially consumes 1 kWh/m³ for each 1° C. increase, this reduces the FO energy requirements (other than pumping costs) to less than 2 kWh/m³, almost 30% lower than the most energy efficient RO process currently in use.

A great quantity of energy can be potentially obtained when waters of different salinities are mixed together. The harnessing of this energy for conversion into power can be accomplished by means of Forward Osmosis, which can be configured as a Pressure Retarded Forward Osmosis (PRFO) system, a Pressure Assisted Forward Osmosis (PAFO) system, or a Pressue Equalized Forward Osmosis (PEFO) system. Embodiments of the invention described herein include a PRFO system, but other forward osmosis systems could be used. Pressure retarded forward osmosis uses a semi-permeable membrane to separate a less concentrated solution, or solvent, (for example, fresh water) from a more concentrated and pressurized solution (for example sea-water), allowing the solvent to pass to the concentrated solution side. The additional volume increases the pressure on the permeate side, which can be depressurized by a hydro-turbine to produce power—thus the term ‘osmotic power’.

The concept of harvesting the energy generated from mixing waters of different salinities was first reported by Pattle, and then re-investigated in the mid 1970s. With recent advances in membrane technology, there has been a reduction in membrane prices, rendering PRFO more economically viable. Encouraged by new research findings, Statkraft, Norway opened the world's first PRFO power plant prototype in November 2009 in Norway, at a site where river water flows into the North Sea, giving the required salinity and osmotic differential against seawater. This prototype has proved that the PRFO concept can be used to generate electricity. The plant was used to test different types of membranes and plant configurations and has been a key factor in the investigation of osmotic power. Despite membrane, hydraulic and generator inefficiencies, it was discovered that approximately 1 MW of power could be generated per cubic meter of river water flow per second into the ocean.

The equation for ideal hydro-dynamic calculations for the power generated by a hydro-turbine is: P=Q*H/k, where P=power in KW, Q=flow rate in GPM, H=static head in feet, and k=5,310 gal·ft/min·kW. A 100 atm difference in osmotic potential between two solutions computes into a static head of almost 3,210 ft (1 atm=9.783 m; 1 m=3.281 ft). The difference in osmotic potential between two solutions, separated by a semi-permeable membrane, yields a pressure differential, which is similar to the effect of gravity in creating potential energy for further conversion to work. Normal hydropower plants use the static head of water in dams to yield energy when the water is allowed to run through turbine generators. Similarly, osmotic pressure differentials can be used to drive turbine generators to create energy.

If we assume an osmotic differential of 100 atm between the concentrated draw solution and the water feed solution, for a 100 GPM flow, the possible power rating of a turbo-generator is 60.45 KW, at 100% efficiency [P=(100 GPM)×(3210 ft/5310 gal·ft/min·KW)]. If the now diluted draw solution is brought back to its original concentration, using renewable energy, (either from solar heat or solar-electricity/wind-electricity) for re-cycling back to the PRFO system, an efficient hydro-electric energy storage system would be feasible, similar to conventional pumped hydro-electric storage, but without the geographical limitations and environmental issues associated with huge dams and reservoirs.

Examples of embodiments of the present inventive energy storage technology are shown in FIGS. 1 and 2, using both ionic osmotic solutions and polymeric (e.g., cloud-point) osmotic draw solutions. Referring to FIG. 1, the use of ionic osmotic draw solutions in an FO system, for example a Pressure Retarded Forward Osmosis (PRFO) system, is shown, integrated with a CEDI system, for storage of renewable energy from solar photovoltaics or wind energy, and generation of power using hydro-turbines as needed by utilities, and commercial and industrial consumers. Referring to FIG. 2, the use of polymeric (e.g., cloud-point) osmotic solutions in a PRFO mode is shown, integrated with solar-thermal systems, to store renewable energy and generate power as needed by utilities, and commercial and industrial consumers.

Ionic Osmotic Solutions:

A 25% MgCl₂ solution has an osmotic potential of 400 atm, equivalent to almost 12,839 feet of head, versus fresh water. At a 50 GPM flow rate across a PRFO membrane system, the possible power rating would be equal to 116.66 KW [P (KW)=50*12,839/5310]. Higher concentrations of the ionic salt in water also exhibit higher osmotic potentials: thus, a 50% MgCl₂ solution exhibits an osmotic potenila of 1,000 atm. The ability to use higher concentrations of ionic salts is only limited by the capacity of the CEDI system to substantially regenerate these concentrations during the energy storage cycle.

At a 50 GPM rate, the volume of water needed to generate power is around 72,000 gallons, for a 16-hour power production cycle for the 100 KW system (if including energy inefficiencies). Given that the concentrated MgCl₂ solution is run against essentially fresh water, and the permeate is a diluted MgCl₂ solution, if the time taken for re-concentrating the MgCl₂ solution by the CEDI system is 6 hours (time taken for renewable power generation), the needs of energy production/storage and generation can be suitably matched.

Referring to FIG. 1, one embodiment of an inventive system 10 comprises an FO system 12, a hydro-turbine 14, and a multi-cell electro-deionization system 16, with optional storage vessels 20, 22 and 24, and an optional second hydro-turbine 28. Preferably, the electro-deionization system 16 is a continuous electro-deionization system and is preferably powered by natural renewable energy, such as solar or wind. Other means of powering the electro-deionization system 16 are contemplated, however, whether natural or renewable or not.

In one embodiment, the FO system 12 is configured as a PRFO system, although it could also be a PAFO system or a PEFO system. In any case, the FO system 12 comprises a semi-permeable membrane 30, in which draw solution 32 is directed along one side and a water-rich mixture 34 is directed along the other side of the membrane 30. The draw solution 32 draws water across the membrane 30 from the water-rich mixture 34, creating a diluted draw solution 36, which can be directed into the hydro-turbine 14. If desired the diluted draw solution 36 can be stored in a storage vessel 16 before being introduced into the electro-deionization system 16. The electro-deionization system 16 is configured to separate the draw solution from the water, either or both of which can be stored in a storage vessel, 18, 20. The regenerated draw solution 32 can then be directed into the FO system 12. The water rich mixture 34 can be directed through a second hydro-turbine 24 before being introduced into the FO system 12. In one embodiment, the draw solution comprises an ionic salt, such as MgCl₂. Other ionic solutions are contemplated, as described above.

Still referring to FIG. 1, in one mode of operation, during a period of renewable energy production, for exampe, the diluted draw solution of the ionic salt (e.g., MgCl₂) is routed from the storage tank through the CEDI system, wherein the electricity produced from the renewable energy source (solar or wind electric power) is used to re-concentrate the ionic salt solution to, e.g., 25% MgCl₂, and also to simultaneously separate the majority of water from the diluted draw solution into a fresh water tank. These two streams are stored in separate tanks for subsequent use in the power production cycle. The energy storage cycle, thus, essentially consists of the regeneration process of a concentrated ionic osmotic draw solute for use in a forward osmosis system, such as the PRFO system, for subsequent power generation. When power generation is needed, the regenerated and concentrated MgCl₂ solution is pumped through the draw side of the FO membrane system, while the fresh water is routed through a hydro-turbine, preferably a gravitational vortex hydro-kinetic device to take advantage of the Coriolis effect, to the feed side of the FO membrane. The high difference in osmotic potentials between these two streams enables large volumes of water to permeate across the membrane, which in turn is routed through a conventional hydro-turbine, to produce power as needed. The use of two hydro-turbines is optional, but enables optimization of the power produced and increased efficiency for the full cycle.

Referring to FIG. 2, one embodiment of an inventive system 110 comprises an FO system 112, a hydro-turbine 114, a heat exchanger 116, and a solvent-water separator 118, with optional storage vessels 120, 122, 124, and an optional second hydro-turbine 128. Preferably, the heat exchanger 116 receives heat from natural renewable energy, such as solar. Other heat sources for the heat exchanger 116 are contemplated, however, whether natural or renewable or not, including using waste heat, as described in U.S. Ser. No. 15/675,663 dated Aug. 11, 2017, and assigned to NRGTEK, Inc., the entire contents of which is incorporated by reference in its entirety herein.

In one embodiment, the FO system 112 is configured as a PRFO system, although it could also be a PAFO system or a PEFO system. In any case, the FO system 112 comprises a semi-permeable membrane 130, in which draw solution 132 is directed along one side and a water-rich mixture 134 is directed along the other side of the membrane 130. The draw solution 132 draws water across the membrane 130 from the water-rich mixture 134, creating a diluted draw solution 136, which can be directed into the hydro-turbine 114. If desired the diluted draw solution 136 can be stored in a storage vessel 120 before being introduced into the heat exchanger 116. The heat exchanger 116 is configured to heat the draw solution above a certain separation temperature, so that the diluted draw solution can be directed to the solvent-water separator 118 for separating the draw solution 132 from the water-rich mixture 134, either or both of which can be stored in a storage vessel, 122, 124. The regenerated draw solution 132 can then be directed into the FO system 112. The water rich mixture 134 can be directed through a second hydro-turbine 128 before being introduced into the FO system 112. In one embodiment, the draw solution comprises a polymer, such as such as a cloud-point polymer. Various polymers are contemplated, as described herein.

Still referring to FIG. 2, in such embodiments, the use of polymeric (e.g., cloud-point) osmotic agents can be used for energy storage. During the period of renewable energy generation, the diluted draw solution is routed from the storage tank to a solar-thermal system, wherein temperatures in excess of the cloud-point temperatiure of the organic solute is reached, causing phase separation of the solute from its water mixture. This dual-phase mixture is routed through a liquid-liquid separation system, and the concentrated draw solute routed to a storage vessel, while the now substantially water-rich portion is routed to a separate storage vessel. The energy storage cycle, thus, essentially consists of the regeneration process of a concentrated ‘cloud-point’ osmotic draw solute for use in the PRFO mode for subsequent power generation.

When power generation is needed, the regenerated and concentrated ‘cloud-point’ organic solution is pumped through the draw side of a FO membrane system, while the fresh water is routed through a hydro-turbine, preferably a gravitational vortex hydro-kinetic device to take advantage of the Coriolis effect, to the feed side of the FO membrane. The high difference in osmotic potentials between these two streams enables large volumes of water to permeate acorss the membrane, which in turn is routed through a conventional hydro-turbine, to produce power as needed. The use of two hydro-turbines is optional, but enables optimization of the power produced and increased efficiency for the full cycle. Examples of cloud point draw solutions, including cloud point glycols, are described by example only in U.S. Pat. No. 8,021,553, U.S. Ser. No. 15/153,688 filed May 12, 2016, and U.S. Ser. No. 15/272,406, filed Sep. 21, 2016, each of which is incorporated by reference herein in their entireties.

Using commercially available carbon nanotube FO membranes from Porifera, a PFO-9S system has a membrane surface area of 67 m². For a feed concentration of 1M NaCl (osmotic potential of 48 atm) against pure water, the flux rate of water across the membrane was measured at 33 liters/m²/hr (LMH). For a 25% MgCl₂ solution (osmotic potential of 400 atm, 2.6M solution of MgCl₂) against fresh water, a flux rate in excess of 150 LMH is feasible. Thus, across the PFO-9S membrane, the total water flux would be around 10,050 liters/hr, or 2,655 gallons/hr. This equates to 44.25 GPM. The equivalent head for an osmotic potential of 400 atm is 12,842 feet of water. Computing the power rating of such a system, a water flux of 44.25 GPM and an osmotic differential of 400 atm, the power rating of a PRFO system is equivalent to 107 KW [P(KW)=44.25*12,842/5310=107 KW].

The PFO-9S membrane is available at a retail cost of $25,000, and assuming a balance of plant cost (including the CEDI system and the hydro-turbines) of $125,000, we have a total cost of $150,000 for a 100 KW, with a capacity of sufficient energy storage for an 18-hour generation system (using approximately 60,000 gallons of water and concentrated draw solutions). Thus, the cost of storage is $150,000 for 1,800 kWh, i.e., $83.33/kWh. Assuming a 10-year life for the system (3650 cycles), the life-cycle cost of storage ($/kWh/cycle) computes to $0.0228/kWh/cycle. In comparison, for lithium-ion batteries (LIBs), the life-cycle cost of storage for a 10-year period is as follows: in the case of a LIB system specifying 6.4 kWh for $3,000, we have $468.75/kWh of storage capacity; in the case of a LIB system at $1,600, for 2.2 kWh it is $727.27/kWh of storage capacity. The LIB system commonly has a 10-year warranty, i.e. a full warranty for 3,650 Full Depth of Discharge cycles (once a day for 10 years), with zero capacity fade. For these above examples of LIBs, the Cost/kWh/Cycle computes to: $468.75 kWh/3,650 cycles=$0.1284 cents/kWh/cycle; and $727.27 kWh/3.650 cycles=$0.1992 cents/kWh/cycle. Thus, embodiments of the present invention can provide economic benefits to renewal energy storage.

Persons of ordinary skill in the art may appreciate that numerous design configurations may be possible to enjoy the functional benefits of the inventive systems. Thus, given the wide variety of configurations and arrangements of embodiments of the present invention the scope of the invention is reflected by the breadth of the claims below rather than narrowed by the embodiments described above. 

What is claimed is:
 1. A renewable energy storage system comprising: a forward osmosis system for drawing water across a membrane such that, when in use, the water drawn across the membrane is used to dilute an osmotic draw solution and the diluted osmotic draw solution is used to drive a hydro-turbine to produce energy; a hydro-turbine driven by the diluted draw solution when in use, and a separation system for separating the drawn water from the draw solution, the separation system powered by one or more natural regenerating energy sources, so that the draw solution can be re-directed to the forward osmosis system and the water can be reused to be drawn across the forward osmosis membrane.
 2. The renewable energy storage system of claim 1, wherein the separation system comprises an electro-deionization system.
 3. The renewable energy storage system of claim 2, wherein the electro-deionization system comprises a continuous electro-deionization system.
 4. The renewable energy storage system of claim 1, wherein the one or more natural regenerating energy sources comprises either solar energy and/or wind energy.
 5. The renewable energy storage system of claim 1, further comprising a second hydro-turbine.
 6. The renewable energy storage system of claim 1, wherein the draw solution comprises one or more ionic osmotic solutions.
 7. The renewable energy storage system of claim 6, wherein the ionic osmotic solution comprises magnesium chloride and/or ammonia chloride.
 8. The renewable energy storage system of claim 1, wherein the forward osmosis system comprises a pressure-retarded forward osmosis system.
 9. A renewable energy storage system comprising: a forward osmosis system for drawing water across a membrane such that, when in use, the water drawn across the membrane is used to dilute an osmotic draw solution and the diluted osmotic draw solution is used to drive a hydro-turbine to produce energy; a hydro-turbine driven by the diluted draw solution when in use; a solar thermal heat exchanger through which the diluted osmotic draw solution can be directed for purposes of heating up the draw solution to cause substantial separation of the draw solution from the water, and a solvent-water separator configured to separate the draw solution from the water so that the draw solution can be re-directed to the forward osmosis system and the water can be reused to be drawn across the forward osmosis membrane.
 10. The renewable energy storage system of claim 9, further comprising a second hydro-turbine.
 11. The renewable energy storage system of claim 9, wherein the forward osmosis system comprises a pressure-retarded forward osmosis system.
 12. The renewable energy storage system of claim 9, wherein the draw solution comprises a cloud point osmotic solution.
 13. The renewable energy storage system of claim 12, wherein the cloud point osmotic solution comprises one or more cloud point glycols.
 14. A method of storing renewable energy comprising: drawing water across a forward osmosis membrane in a forward osmosis system such that the water drawn across the membrane dilutes an osmotic draw solution; directing the diluted osmotic draw solution to drive a hydro-turbine to produce energy; and separating the water from the draw solution using one or more natural regenerating energy sources so that the draw solution can be re-directed to the forward osmosis system and the water can be reused to be drawn across the forward osmosis membrane.
 15. The method of storing renewable energy of claim 14, wherein separating the water from the draw solution comprises directing the diluted draw solution into a CEDI system powered by the one or more natural regenerating energy sources.
 16. The method of storing renewable energy of claim 15, wherein the one or more natural regenerating energy sources comprises either solar energy and/or wind energy.
 17. The method of storing renewable energy claim 14, wherein separating the water from the draw solution comprises directing the diluted draw solution through a solar thermal heat exchanger for purposes of heating up the draw solution to cause substantial separation of the draw solution from the water, and then directing the diluted draw solution into a a solvent-water separator configured to separate the draw solution from the water.
 18. The method of storing renewable energy of claim 14, further comprising directing the water through a second hydro-turbine before re-directing the water to the forward osmosis system.
 19. The method of storing renewable energy of claim 14, wherein the forward osmosis system comprises a pressure-retarded forward osmosis system.
 20. The method of storing renewable energy of claim 14, wherein the draw solution comprises one or more ionic osmotic solutions or one or more cloud point osmotic solutions. 